Brief Description of the Prior Art
Upon preparation of solid foodstuffs such as cheese or the like using soybean protein, various problems caused by heating have been pointed out heretofore.
For example, in Published Examined Japanese Patent Application No. 6107/1974, there is described a method for producing processed cheese-like foodstuffs which comprises kneading a mixture mainly composed of soybean protein isolate having a low gelation ability, casein (preferably, water-soluble casein) [preferred ratio of both is 1 : (1 to 0.5)] and oils and fats while adding water to the mixture without heating, then sealing the kneaded mixture in a casing, and heating to cause gelation. According to this method, it is important to conduct the kneading without heating; it is described that if the kneading is performed with heating, gel of soybean protein formed by heating is destroyed by mechanical agitation operation and it thus becomes impossible to form a continuous phase of tight protein so that the tissue of the product becomes sandy and cheese-like foodstuffs cannot be obtained.
Further in Published Unexamined Japanese Patent Application No. 146237/1983 there is described a method for producing cheese-like foodstuffs which comprises kneading protein mainly composed of vegetable protein (preferably soy protein isolate) (which may also contain sodium caseinate, etc. in a half amount or less than the amount of protein) with oils and fats and water and allowing the mixture to stand at 0.degree. to 60.degree. C. for 20 minutes or longer thereby to cause gelation. It is described there that when the kneaded matter is heated, texture of the product becomes dry and crumbly and lacks smoothness, and the product shows poor melting feel to the tongue.
Further it is pointed out in Published Unexamined Japanese Patent Application No. 108333/1986 that by referring to the method as described in Published Examined Japanese Patent Application No. 6107/1974 described above, the product mainly composed of soybean protein provides dry and crumbly texture but lacks cheese-like smoothness; and by referring to the method described in Published Unexamined Japanese Patent Application No. 146237/1983 described above, vegetable protein is hydrated only with difficulty due to poor affinity of the vegetable protein to water so that protein particles remain to provide poor touch to the tongue and bad texture. It is thus described in Published Unexamined Japanese Patent Application No. 108333/1986 that the method of adding protein, oils and fats and acids simultaneously and then agitating, the method of agitating protein and oils and fats while adding water thereto, etc. are not suitable; and good solid foodstuffs are obtained only in the case that raw materials are mixed in a specific order, namely, phosphates and/or citrates (if necessary, table salt in addition thereto) to water, dissolving the mixture, heating the solution, adding protein, edible oil and fats and organic acids in this order and stirring the mixture. According to this method, the addition and agitation of these raw materials are carried out with heating.
As a result of investigations made by the present inventors relative to the prior art described above, it has been found that the methods described in Published Examined Japanese Patent Application No. 6107/1974 and Published Unexamined Japanese Patent Application No. 146237/1983 encounter difficulties that the methods do not make the best use of good physical properties possessed by casein, since these methods are quite different from the mixing action upon melting with heating while agitating with melted salts during conventional steps of manufacturing processed cheese. In addition, these methods involve a serious restriction in using rennet-casein that has the most excellent flavor among the casein. In particular, the method described in Published Unexamined Japanese Patent Application No. 146237/983 does not involve heating to 60.degree. C. or higher at steps subsequent to a kneading step so that there is a problem in storability of the product.
Further the present inventors have already found a method which eliminate difficulties of causing separation or protein particles remaining during the manufacturing steps or failing to give products, etc., without relying upon the specific addition method described in Published Unexamined Japanese Patent Application No. 108333/1986 [method which comprises adding phosphates and/or citrates (if necessary, additionally adding table salt thereto) to dissolve them, then adding in this order, protein, oils and fats and oganic acids and agitating the mixture]. However, the solid foodstuffs produced by these methods have defects that as the amount of the soybean protein used increases, texture around the tooth dissimilar to cheese might be caused or plasticity like clay becomes predominant to reduce elasticity of the bodies, and if such becomes markedly serious, a solid body cannot be obtained. The present inventors have come to recognize that these defects should be removed.
As a result of extensive investigations aiming at preparing solid foodstuffs having good texture mainly composed of soybean protein, casein, water and oils and fats via steps of heating and agitation, the present inventors have accomplished the present invention.